The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A dual-overhead camshaft internal combustion engine (ICE) includes intake and exhaust camshafts. The camshafts are driven by a crankshaft via a timing element. The timing element may include a timing chain or timing belt. Rotation of the camshafts actuates respective intake and exhaust valves relative to an angular position of a crankshaft. Position and timing of the camshafts is controlled during engine operation. Camshaft position and timing characteristics may be determined during an engine synchronization event. An engine synchronization event may occur during an engine startup event.
An engine startup begins when an ignition system of a vehicle is activated, for example, when an ignition key is rotated to an ON position. A vehicle electrical system supplies power to an engine control system when the ignition system is activated. The engine control system causes an engine crank event and an engine synchronization event to occur. The engine is cranked during the crank event to start the engine. A camshaft position sensor is used along with the crankshaft position sensor in order to determine engine position. This is referred to as engine synchronization. Determining engine position refers to determination of piston positions relative to crankshaft and camshaft positions as measured by crankshaft and camshaft sensors. After engine start, the camshaft home positions may be learned relative to the crankshaft position. If the crankshaft home positions are not within a calibratable specification, an engine diagnostic trouble code (DTC) is set. This is referred to as a “mis-build” detection or fault. A mis-build may be detected using an engine diagnostic process.
An engine control system may include camshaft phaser(s). The camshaft phaser(s) may be used to adjust angular positions of camshafts relative to each other and/or relative to a crankshaft. This is referred to as “phasing” of the camshafts. Fixed phase relationships between angular positions of the camshafts and the crankshaft are maintained based on engine design when the engine is in an OFF state. The fixed phase relationships may be adjusted during engine operation by introducing variable phase offsets between the camshafts and/or the crankshaft. The variable phase offsets alter timing of intake valves and/or exhaust valves.
While camshaft phasing can enable various advanced engine control features, camshaft positions relative to a crankshaft need to be accurately determined for engine control. An erroneous determination of camshaft position may result in false indication of a mis-build.
Camshaft positions relative to a crankshaft may be determined when the camshafts are maintained in respective “home” or “parked” positions. A home position refers to a preset angular position of a camshaft relative to a crankshaft when an engine is in an OFF state. A camshaft may be rotated by a camshaft phaser relative to a crankshaft, and away from the home position when the engine is in an ON state. A parked position refers to an angular position of a camshaft after a camshaft phaser restores the camshaft to the home position. Absent an error or aberration in engine operation, the parked position is the same as the home position.
A process for determining a camshaft home position is referred to as a “camshaft home-learn”. One implementation of a camshaft home-learn includes estimating a camshaft home position when the camshafts are maintained in respective home positions during an engine startup mode. The estimate may be updated until variance in averages is within a predetermined error range. Although this averaging process provides an accurate estimate of a camshaft home position, the camshaft needs to be maintained in the home position throughout the averaging process.